Instrument lighting device



June 19, 1962 T. STEARNS 3,040,158

INSTRUMENT LIGHTING DEVICE Filed Sept. 25, 1957 4 Sheets-Sheet 1INVENTOR. ZWoIe A ra/y 5215mm BY W June 19, 1962 'r. STEARNS 3,040,163

INSTRUMENT LIGHTING DEVICE Filed Sept. 25, 1957 4 Sheets-Sheet 2 INVENTOR. 7770/9/10 JA STE/7616 BYW a June 19, 1962 T. STEARNS INSTRUMENTLIGHTING DEVICE 4 Sheets-Sheet 5 Filed Sept 25, 1957 June 19, 1962 T.,STEARNS INSTRUMENT LIGHTING DEVICE Filed Sept. 25, 1957 4 Sheets-Sheet4 15.24. R25- m //4 m //6 INVENTOR. fla /v72 5259mm arraa/m Unite'dsiatsPatent My invention relates to a non-glare illuminatin means forilluminating displays such as aircraft instrume ts, and morespecifically relates to a non-glare illuminatin means of the so-calledwedge type which gives a uniformly distributed illumination of adisplay. i

Wedge lighting for devices such as aircraft instruments is well known inthe art and com-prises the use of a transparent wedge-shaped body whichis positioned in front of a display such as an aircraft instrument dialand in a plane substantially parallel to the plane of the dial. A

light rays after they are within the wedge, or to control or extend theangular distribution of the light rays by light source is placed at thewide base of the wedge and light rays are directed from the wide basetowards the apex of the wedge.

More specifically, light rays entering the wedge base and impinging onthe sides at angles greater than the critical angle of total reflectionwill receive multiple total reflections from the inner surfaces of thewedge. With each successive reflection, the rays will approach the nextsurface at a lesser angle until they impinge upon a surface at an anglewhich is less than the critical angle for,

surface. Clearly, the light which emerges from the side djacent the dialsurface or display surface will serve to illuminate the display, whilethe light emerging from the opposite side of the surface will emerge asglare.

in order to eliminate at least a portion of this glare it is possible toplace a second wedge adjacent the first wedge with its apex adjacent thebase of the first wedge. When the wedges are in this relation the lightwhich normally emerges as glare will now be impinged upon the secondwedge and, because of refraction, will impinge the wedge materialwhereupon they will emerge from that upon the opposite surface of thesecond wedge at an angle which is greater than the critical angle. Therays will then undergo multiple internal reflections at successivelygreater angles going down the secondwedge and towa-d its base where itmay be trapped in a light trap,

or may be utilized to illuminate a second display.

One of the major difficulties with the above noted type of wedgelighting system is that the dial surface is not uniformly lighted, butthe lighting is more intense at the lower dial portions adjacent theapex side of the first wedge.

The primary reason for this non-uniformity is that an insufficientlywide range of light rays enters the wedge at its upper and wide portionsand thus few or no rays impinge uponthe inner surfaces near the base atan angle which is less than the critical angle to emerge and therebyimpinge upon the display to be illuminated.

Therefore, the upper portion of the dial or display is not illuminatedto the same intensity as are the lower portions which are illuminated byrays which enter the base of the wedge at an angle which is greater thanthe critical angle and approach the critical angle after a plurality ofreflections within the wedge so as to thereafter emerge from the wedgeto illuminate the lower por tions. That is to say, light does not escapefrom the region close to the base of the wedge because the angular rangeof the rays entering is normally insuflicient to include rays whichemerge before undergoing several internal reflections.

The principle of my invention is to control or extend the angular rangeof the rays entering the base of the wedge or to control or extend theangular range of the combinations of both of these means, thus to securemore efficient and uniform illumination of the display.

In one embodiment of my invention the base portion of the wedge couldbe'corrugatcd to thereby assure that substantially all. light raysimpinged upon the wedge base will be distributed internally so as toemerge equally throughout the length of the wedge.'

In another embodiment of my invention it may be sufiicient to roughenthe surface of the base whereby each roughened particle will serve as asecondary source sending out rays in all directions within the materialof the wedge.

In each of the two embodiments above described a small portion of thewedge surface may be coated with a reflecting material which willoperate as a secondary source within the wedge material. Thus, the lightrays which enter through the corrugated portions of the wedge or theroughened surface of the wedge will have at least a portion thereofimpinged upon the reflecting material which will operate as a secondarysource primarily for illuminating the. upper portion of the display.

- In the circular shaped display, I have further found that theuniformity of lighting over the dial surfaces is increased by making onesurface of the first wedge concave and the adjacent surface of thesecond wedge convex. This increases the angle between the wedge surfaceclosest to the light source thus requiring fewer successive internalreflections to achieve incidence angles less than critical in thisregion of the wedge. This increases the illumination adjacent to thelamps. In addition, this always has the effect of making the centersection of the wedge thinner than the edge in a region extending abovethe light sources toward the thickest point of the edge so that thewedge distributes some light above the light sources in the normalmanner.

It has been further found that the surface at which light enters theround wedge devices may be concave rather than grooved while stillachieving the desired uniform lighting. The concave shape, however, iseasily polished and this feature aids in concealing the light sourcefrom an observer viewing the display.

It is to be noted that this problem has been dealt with in the past byforming the wedge to have an obtuse angle between the base and thesurface adjacent the display. This construction allows the upper displayareas to be illuminated, since it allows rays to enter the upperportions of the dial at the critical angle. However, in thisconstructiomthe angular range of light rays which can be supplied by thelight source is limited by theoretical Accordingly, the primary objectof my invention is to provide a novel non-glare illuminating means forilluminating displays.

Another object of my invention is to provide a novel illuminating meansfor uniformly illuminating displays.

Another object of my invention is to provide a wedge type lightingilluminating means which achieves uniform illumination over thesubstantial length of wedge.

Another object of my invention is to provide a wedge type illuminatingmeans wherein the heavy base portion of the wedge is adapted withsecondary reflecting surfaces for achieving a uniformity in theillumination of the upper as well as the lower portions of the wedge.

A still further object of my invention is to provide a double wedgeillumination system which uniformly illuminates a display andsubstantially decreases glare.

A further object of my invention is to provide a double wedgeilluminating system for both rectangular and circular displays.

Another object of my invention is to provide a secondary emittingsurface on the heavy portion of a wedge for illuminating a circulardisplay wherein the light sources are positioned below the said heaviestportion of the wedge.

Another object of my invention is to provide a double wedge lightingsystem wherein the first wedge has a convex surface and the second wedgesurface adjacent said FIGURE 16 shows a side view of a previously usedtype of wedge.

FIGURE 17 shows a side view of FIGURE 16 and schematically illustratesthe manner in which illumination is distributed across the surface of adial associated with the wedge.

FIGURE 18 is similar to FIGURE 11 and illustrates the convex surface ofthe wedge constructed in accordance with my invention.

FIGURE 19 is a side view of FIGURE 18 and illustrates the manner inwhich the convex surface more uniformly distributes the lighting of thedial associated with the wedge of FIGURE 18.

Referring now to FIGURES 1, 2a, 2b, 2c and 2d, it is desired toilluminate a first and second display 20 and 22 respectively whereindisplay 20 comprises a first, second and third longitudinal displayassociated with pointers 24, 26 and 28 respectively, while display 22 isa drum type display which is rotatable around an axis therethrough.

Instruments of these types are well known in the art and will not bedescribed more fully hereinafter.

first surface is concave to further improve uniformity of lighting acircular display.

These and other objects will become apparent from the followingdescription when taken in conjunction with the drawings, in which:

FIGURE 1 is a perspective view of a first and second wedge constructedin accordance'with my invention when positioned in front of arectangular display.

FIGURES 2a, 2b, 2c and 2d are each side views of the device of-FIGURE 1and schematically illustrate light rays proceeding down the length ofthe wedges to be irrpinged upon a display.-

FIGURE 3 shows the Wedge of FIGURES l and L. which have corrugatedsurfaces as being further provided with secondary reflecting surfacesfor achieving a more uniform distribution of lighting for the display ofFIG- URE 1.

FIGURE 4 is a side view of FIGURE 3.

FIGURE 5 is a perspective view of a circular display having illuminatingmeans positioned in the corners of a square which would contain thecircular display.

FIGURE 6 shows a front view of the second wedge of FIGURE 5.

FIGURE 7 shows a view of FIGURE 6 when taken across the lines 77.

FIGURE 8 is a front view of the first wedge adjacent to the dial surfacein FIGURE 5.

FIGURE 9 is a top view of FIGURE. 8.

FIGURE 90 shows a view of FIGURE 8 when seen in the direction of thearrows 911-90.

FIGURE 10 is a side view of FIGURE 8.

FIGURE 11 is a cross-sectional view of FIGURE 8 when taken across thelines 11-11 and specifically shows the possible curvature which could beimparted to the surface of the wedge of FIGURE 8.

FIGURE 12 is similar to FIGURE 11 and specifically illustrates theoperation of theacute angle formed between the dial surface and thewedge base in conjunction with the reflecting material fastened to thetop surface of the wedge.

FIGURE 13 is a side view of FIGURE 12 specifically illustrating themanner in which the reflecting surface is applied to the base of thewedge.

FIGURE 14 shows another manner in which the wedge of FIGURES 8 and 12could be constructed in conjunc- ItJion with a reflecting materialimpressed upon the wedge ase.

FIGURE 15 is a side view of FIGURE 14.

Positioned in front of these displays are a first and second wedge 30and 32 respectively having their apices adjacent the base of theopposite wedge. In accordance with my novel invention, the base of thefirst wedge 30 which is adjacent to the dial 20 which is to beilluminated is corrugated, as seen by the slots 34, 36 and 38 runningacross the top of the base.

Positioned above this corrugated base, as best seen in this reflectingstrip being a strip of white paint, a eoat-- ing of white ceramic, orany other material which would be a good reflector and is in intimatecontact with the glass surface of the prism.

In operation, the light of the light sources 40 through 46 will enterthe first wedge 30 and that portion of-the light which emerges from thedial side of the wedge will illuminate the dial.

The portion of the light which emerges from the opposite side of thefirst wedge, however, enters the upper portion of the outer wedgewhereby some of this light is trapped by the blackened edges of theOuter wedge, as indicated in FIGURE 1 by a stippled area, while theremainder emerges from the dial side of the lower portion of the outerwedge to illuminate the cylindrical display 22. The remainder of thelight will emerge from the front side of the outer wedge as stray light.

The operation of my novel wedge is more specifically set forth inFIGURES 2a, 2b, 2c and 2d wherein each of the figures trace the path ofa first and second ray which are progressively further down the lengthof the wedge. Thus in FIGURE 2a, light rays from bulb 40 which entersthe corrugated surface of the wedge is shown in solid lines 52 and 54.Light rays 52' and 54 enter the wedge and are totally reflected from theopposing surfaces of the wedge since they strike the surfaces at anangle which is greater than the critical angle.

After the first reflection light ray 54 achieves an angle which is lessthan the critical angle so that a ray 56 emerges from the wedge toimpinge upon dia'. 20. The remainder, or refiectcd light of ray 54, seenas a short dotted line 58, emerges from the opposite side of the dialsurface and enters the second wedge 32. A portion of the ray 58 whichenters wedge 32 is internally reflected as is seen by the long dashedline 60, while the other portion of ray 58 emerges from the second wedgeas stray light indicated by light ray 62.

Light ray 52 has a similar course to that of light ray 54 where theeffective illuminating light of ray 52 emerges as ray '64 impinging upondial surface 20.

Of the light which was reflected in the second we: go 32 and indicatedby the long dashed line, it is seen that upon subsequent reflectionsthis light approaches the sarface of the wedge at an angle which isincreasingly greater than the critical angle required for emergence oflight from the surface so that the light rays in the second wedge willexecute multiple complete reflections until they reach the bottom of thewedge to emerge from the bottom of the wedge and illuminate the seconddisplay 22.

In order to increase the illumination of display 22, it is possible toprovide an auxiliary reflecting surface 66 which receives emerging lightthat would normally not be impinged upon the display 22. Whatever lighttravelling down wedge 32 is not utilized in illuminating display 22 willbe trapped in the blackened surface of the second wedge edges, as hasbeen seen in FIGURE I.

FIGURE 2b shows a trace of rays which will be emitted from light source40 which will be reflected a plurality of times until they achieve thecritical angle required for emergence from the wedge surface to thatrays 68 and 70 eventually emerge to illuminate a lower portion of thewedge, and in a similar manner, FIGURES 2c and 2d show the path of otherlight rays which will eventually emerge as rays 7274 and 76--78respectively, which illuminate still lower portions of the dial surface.

It is to be noted that the solid lines in each of FIG- URES 2a through2a represent the initial light ray emitted by the source, while theshort dotted lines represent the path of remaining light after the lightray achieves its critical angle.

Thus, it is seen that by using my novel corrugated surface or roughenedsurface which causes a dispersion of the light as it enters the wedge, Ican achieve a uniformity of illumination along the total length of thedial 20. In the past, as has been described above, it has been necessaryto utilize a complex wedge construction of appreciable width at the basein order to have the rays of FIGURE 2a be useful rays which can operateto illuminate the upper portions of the dial surface.

If, in addition to the corrugated surface, the secondary source ofFIGURE 3 were utilized so that light impinging upon strips 48 and 50were reflected, then it is clear that a large portion of all the lightwhich enters the wedge surface, regardless of its angle, will beutilized in illuminating dial 20 in a substantially uniform manner withthe remainder illuminating display 22, with a very small portion oflight being emitted as glare from lthe last surface of the second wedge.

It is important to note however that it is not essential to usecorrugations if the secondary strips 48 and 50 are used. Furthermore,these strips 48 and 50 could be white ceramic coatings for diffusion oflight impinged thereon, or reflecting coatings for actual reflection oflight impinging thereon. If desired, one strip could be used and thisstrip could be the coated surface (not shown) of a separating memberwhich separates two wedges when the double wedge is used.

FIGURES 1, 2a through 211, 3 and 4 have shown my novel invention inconjunction with a rectangular display. FIGURE 5 shows a perspective,view of the manner in which my novel invention may be utilized inconjunction with a round display.

FIGURE 5 is more specifically comprised of a round dial 80 having apivotally mounted pointer 82 rotatable with respect therewith. As wasthe case in FIGURE 1, illumination of dial 80 is achieved by means of afirst and second wedge 84 and 86 respectively which have their apicesadjacent the base of opposite wedges.

The second wedge 86 is seen in a side cross-sectional view in FIGURE 7,while FIGURE 6 shows a front view of wedge 86. FIGURE l, the outersurfaces of wedge 86 of FlGURE 5 are blackened in any desired manner soas to prevent the revelation of stray light, this blackening beingschematically indicated by the stippled area.

As was the case of the second wedge of.

sources for illuminating display of FIGURE 5 are,

positioned in the corners of a square in which the round display 80would fit so as to conserve space, these light sources being seen asbulbs 88 and 90.

Light sources 88 and are positioned adjacent portions 92 and 94 in thebase of prism 84 whereby wedge action, as above described in FIGURES 2athrough 2d,

will occur only for wedge portions below the level of light sources 88and 90.

Thus, in a circular type of wedge, it is seen that the dial portionswhich are above the level of light sources 88 and 90 will not beilluminated.

That is, even though the portions 92 and 94 of the base of the firstprism adjacent the display are constructed to be corrugated, theportions above the light sources still will not receive any substantiallighting.

In accordance with my invention, however, I have provided a secondaryilluminating means, seen in FIGURES 9 and 10 as the reflecting surface96 which receives light coming up the wedge, and diffuses this light b.ck and into the upper dial surface. This reflecting mellium could againbe white paint or white ceramic material, as was the case of thesecondary source material in FIGURES 3 and 4.

In order to further enhance the operation of this secondary source, therear portion of the base may be sloped, as seen by the sloped surface100 in FIGURE 10, the operation of which will be described more fullyhereinafter.

While the base portions adjacent light sources 88 and 90 of FIGURE 5, ormore specifically, portions 92 and 94 of FIGURES 8 and 9, could be ofthe corrugated nature as set forth above, I have found that I can alsoconstruct portions 92 and 94 to have concave polished surfaces such asthe surface 102. of FIGURE 9a.

When the surfaces 92 and 94 are so constructed, 1 have found that Iachieve the same desirable features of uniform lighting below the lineof the light source while still obtaining a surface which is easilypolished. so as to eliminate light spots at the edge of the illuminateddisplay which are caused by irregularities in the surface through whichlight is emitted into the wedge.

The surface of the first wedge 84 which is away from the surface ofdisplay 80 may have a concave curvature, as seen at surface 104 ofFIGURE 11 which cooperates with the convex shaped surface 89 of thesecond wedge 86 of FIGURE 7, thus achieving the results to be set forthhereinafter.

However. surface 104 could be a planar surface cooperating with a planarsurface of the second wedge.

By whitening the upper base portion of. the wedge, as was set forth inFIGURES 8 and 9, I provide a secondary emitting surface which willreflect light coming up the wedge onto the dial 80. Thus, as may be seenin FIGURES l2 and [3, a layer of light reflecting material 96 is adheredto the surface of the prism. Hence. when light strikes the surface ofreflecting material 96. it will be reflected to cause a first portion togo down the prism, as indicated by my 106, while a second ray 108 willbe diffused into the upper portions of dial 80 of FIGURE 5 to therebyilluminate that upper portion of the dial which normally would not beilluminated because it is above the level of the light sources.

The distribution of light intensity at reflecting surface 9 6 isindicated by the length of the arrows within the circle 110 in FIGURE12. Thus, by causing the surface to form an acute angle with respect tothe wedge surface adjacent the dial, the intensity distribution curve isslanted circle 116.

over so that higher intensity rays are emitted towards the upper portionof the dial. If this relatively high in tensity illumination is notrequired at the upper portion of the dial, then the prism need not havethe cut-away portion and may be shaped as set forth in FIGURES l4 and 15where the upper base surface is coated with a reflecting material, asseen at positions 112 and 114.

Here again it is seen that light coming up the wedge will be impingedupon surface 112, and will be reflected with an intensity distributiongiven by'the lines within the Since the acute angle is not provided inthe case of FIGURE 14, however, most of the light which is impinged uponthe upper portions of the dial is re fiected from surface 114, ratherthan from surface 112-. In either'the structure of FIGURE l2 or FIGUREl4 an appreciable portion of the upper dial surface is illuminated. eventhough this portion is above the: light sources.

The effect of having the cooperating surfaces of the adjacent first andsecond wedges respectively concave and convex is best seen in FIGURES 16through 19.

More specifically, FIGURES 16 and 17 show an inner wedge 118 which has aflat surface 3.20 which is adjacent a cooperating flat surface of asecond wedge (not shown). if, in FIGURE 17, the light sourcesilluminating this wedge were point sources i292 and 3124, then thegeneral light distribution across the wedge is seen in the curved linesindicating the discrete bands of illumination from these sources. Notethat this effect of bands is eliminated by using sources of finite sizein an actual case. The dash lines horizontally crossing the figuredepict the sloping surface of the wedge in the same manner as contourlines show hills and valleys on a map.

By forming the wedge surfaces to be cooperating convex and concavesurfaces as shown for prism 34 of FIGURE 18, then the distribution oflight from point sources 122 and 124 is seen to be changed so that thelight reaches more upward portions of wedge 84, as seen in FIGURE 19.Examination of the dashed contour lines shows why this is so since lightfrom the edge is crossing contour lines even when travelling upward fromthe source, contrary to the condition for the planar wedge shown inFIGURES l6 and 17.

That is to say, portions of the dial surface 84) ot'FIG- URE adjacentthe thicker portion of the wedge 84 of FIGURE 18, would be moreilluminated than they would in the case of a pair of wedges havingplanar surfaces.

Thus, it is seen that the construction of my novel illuminating deviceof FIGURE 5 contains many features each of which could .be usedindividually or in any combination.

Although I have described preferred embodiments of my novel invention,many variations and modifications will now be obvious to those skilledin the art, and I prefer therefore to be limited not by the specificdisclosure herein but only by the appended claims.

I claim:

l. A display illuminating device comprising a wedge of substantiallytransparent material positioned in front of said display and a lightsource positioned adjacent a relatively thick portion of said wedge forintroducing light into said wedge; said wedge having arcircular face,said light source being positioned in the corner of a square withinwhich said circular face wedge would fit whereby said light source doesnot appreciably extend the volume required for mounting said circularface wedge; a portion of the thicker portions of the base of said wedgeother than the portion adjacent to said light source being coated with areflecting material for reflecting illuminating light to the portions ofsaid display adjacent the thicker portions of said wedge, said thickerportions of said wedge being further constructed to form an acute anglewith respect to said display.

2. A display illuminating device comprising a wedge of substantiallytransparent material positioned in front of said display and a lightsource positioned adjacent a relatively thick portion of said wedge forintroducing light into said wedge; said wedge having a circular face,said light source being positioned in the corner of a square withinwhich said circular face wedge would fit whereby said light source doesnot appreciably extend the volume required for mounting said circularface wedge; a portion of the thicker portions of the base of said wedgeother than the portion adjacent to said light source being provided withsecondary light distributing means constructed to redistribute at leasta portion of the light of said light source entering said wedge, saidthicker portions of said wedge being further constructed to form anacute angle with respect to said display.

3. A display illuminating device comprising a wedge of substantiallytransparent material positioned in front of said display and a lightsource positioned adjacent a. relatively thick portion of said wedge forintroducing light into said wedge; said wedge having a circular face,said light source being positioned in the corner of a square withinwhich said circular face wedge would fit whereby said light source doesnot appreciably extend the volume required for mounting said circularface wedge; a portion of the thicker portions of the base of said wedgeother than the portion adjacent to said light source being provided withsecondary light distributing means constructed to redistribute at leasta portion of the light of said light source entering said wedge; saidportion of said wedge adjacent said light source having a polishedconcave surface, said thicker portions of said wedge being furtherconstructed to form an acute angle with respect to said display.

4. A display illuminating device comprising a wedge of substantiallytransparent material positioned in front of said display and a lightsource positioned adjacent a relatively thick portion of said wedge forintroducing light into said wedge; said wedge having a circular face,said light source being positioned in the corner of a square withinwhich said circular face wedge would fit whereby said light source doesnot appreciably extend the volume required for mounting said circularface wedge; a portion of. the thicker portions of the base of said wedgeother than the portion adjacent to said light source being provided withsecondary light distributing means constructed to redistribute at leasta portion of the light of said light source entering said wedge; saidsecondary light distributing means including a reflecting material on aportion of the face of said wedge adjacent said base which face is awayfrom the surface of said display, said thicker portions of said wedgebeing further constructed to form an acute angle with respect to saiddisplay.

5. A display illuminating device comprising a first wedge ofsubstantially transparent material positioned in front of said displayand a light source positioned adjacent a relatively thick portion ofsaid first wedge for introducing light into said first wedge; said firstwedge having a circular face, said light source being positioned in thecorner of a square within which said circular face first wedge would fitwhereby said light source does not appreciably extend the volumerequired for mounting said circular face first wedge; a portion of thethicker portions of the base of said first wedge other than the portionadjacent to said light source being provided with secondary lightdistributing means constructed to redistribute at least a portion of thelight of said light source entering said first wedge; and a secondcircular wedge; said second circular wedge having its heavy base portionadjacent the thin apex portion of said first circular wedge, saidthicker portions of said first wedge being further constructed to forman acute angle with respect to said display.

(Other references on following page} 9 UNITED STATES PATENTS Rylsky Ian.30, 1940" Triplctt Sept. 10, 1940 Christensen et a1. May 2, 1944-Gardner Sept. 26, 1950 5 Prideaux et al. July 24, 1951 Levy May 26,1953 1% Nierenbcrg et a1. July 28, 1953 Lazo Aug. 28, 1956 Hudson O91,6,--1 959 FOREIGN PATENTS France Apr. 19, 1943 France Oct. 27, 1954

